1. Field of the Invention
The present invention relates to a receiving circuit, in particular a receiving circuit that receives differential signals and transmits them to a circuit in the subsequent stage.
2. Description of Related Art
Differential signals are often used for signal transmission/reception between semiconductor devices. When an extraneous noise is mixed into differential signals, the extraneous noise equally affects the common-mode components (or common-mode voltages) of the two signals constituting the differential signals. Meanwhile, the receiving circuit that receives the differential signals generates an output signal based on a differential component obtained by removing the common-mode component from the differential signals. By using differential signals for signal transmission in this manner, the receiving circuit can receive transmission data transmitted by the differential component without being affected by extraneous noises.
However, in general, a receiving circuit is constructed by using a differential amplifier. Therefore, in some cases, the receiving circuit could not accurately receive the differential component of differential signals when the common-mode voltage of the differential signals exceeds the common-mode input range of the receiving circuit. Accordingly, Japanese Unexamined Patent Application Publication Nos. 2002-217653 and 2002-314398 and “Easy-to-Use Differential Amplifiers Simplify Balanced Signal Designs—Design Note 333, Linear Technology Corporation (hereinafter, simply referred to as “Design Note 333”)” disclose techniques to extend the common-mode input range of a receiving circuit.
The differential amplification circuit disclosed in Japanese Unexamined Patent Application Publication No. 2002-217653 includes a voltage shift unit located between a differential amplification unit and an input terminal. Then, the differential amplification circuit extends its common-mode input range by shifting the voltage level of an input signal with the voltage shift unit. The semiconductor integrated circuit disclosed in Japanese Unexamined Patent Application Publication No. 2002-314398 detects the common level of differential signals by using a common-level detection circuit. Then, the semiconductor integrated circuit controls the operating current of the differential amplifier by controlling the voltage level of the bias voltage based on the detected common level. In this way, the semiconductor integrated circuit disclosed in Japanese Unexamined Patent Application Publication No. 2002-314398 extends the common-mode input range of the differential amplifier.
However, there is a problem in the differential amplification circuit disclosed in Japanese Unexamined Patent Application Publication No. 2002-217653 that the output of the voltage shift unit is saturated for the common-mode voltage exceeding the power-supply voltage range. Further, the semiconductor integrated circuit disclosed in Japanese Unexamined Patent Application Publication No. 2002-314398 controls only the operating current of the differential amplifier. Therefore, there is also a problem that the common-mode input range cannot be extended over the power-supply voltage range.
Meanwhile, Design Note 333 discloses an example of a differential amplification circuit capable of coping with a common-mode voltage exceeding the power-supply voltage range. FIG. 7 shows a circuit diagram of a differential amplification circuit 100 disclosed in Design Note 333. As shown in FIG. 7, the differential amplification circuit 100 compresses the amplitude level of an input signal Vin by using a voltage-dividing circuit composed of resistors Rg and Rs. Then, the compressed input signal Vin is input to a differential amplifier AMP to obtain an output signal Vout.